This invention relates to an X-ray tube, and more particularly to an X-ray tube with an anode to which the blackening treatment is applied.
In the X-ray tube, X-rays are produced by impingement of electrons emitted from the filament of the focusing electrode of the cathode onto the target of the anode. In this case, approximately 99% of the kinetic energy of the electrons is transformed into heat with the resultant of temperature rise of the target. Thus, how to effectively dissipate the heat produced in the target is one of serious problems in the X-ray tube, and the X-ray output capacity depends largely on the heat dissipation.
From a structural view point, the X-ray tube is classified into two; a stationary anode X-ray tube and a rotating anode X-ray tube. In the case of the stationary anode X-ray tube, the anode is relatively easily cooled with a peculiar construction that the anode including a chip-shaped target is hermetically fixed at one end of an air-sealed envelope. In the rotating anode X-ray tube, a disc-shaped target of the anode rotates in the air-sealed envelope. As a result, a certain portion on the target is subject to the impingement of the electrons and then it dissipates to some degree the heat accumulated therein until it rotates to return to the position where it is again struck by electrons. However, it is in fact difficult to construct the structure sufficiently cooling the anode, since the target rotates at a high speed, e.g. 3000 to 12,000 r.p.m. There is further a high possibility that the heat conducted from the target to the ball bearing for supporting the rotary shaft, deforms the ball bearing. For this, in the rotating anode X-ray tube, the anode is conventionally cooled through the heat radiation from the target, the rotary shaft and the rotor fixed or the rotary shaft.
Known is a rotating anode X-ray tube the outer surface of whose rotor is covered with a black layer of copper sulfide for the purpose of attaining an effective heat dissipation. The copper sulfide layer is bluish black and is insufficient in terms of radiation of the heat rays on the order of 4 .mu.m wavelength, occupying the most part of the amount of heat rays produced in the X-ray tube. Therefore, the heat radiation characteristic of the above-mentioned X-ray tube is insufficient for a large capacity X-ray tube.
Thus, in the X-ray tube, more particularly in the rotating anode X-ray tube, there has earnestly been desired an advent of the X-ray tube having a high heat radiation characteristic permitting an effective anode cooling. Also, in the stationary anode X-ray tube, a high heat radiation characteristic of the anode is preferable because it advantageously assists the cooling.